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.Dd $Mdocdate: July 15 2022 $
.Dt FIDO_CRED_SET_AUTHDATA 3
.Os
.Sh NAME
.Nm fido_cred_set_authdata ,
.Nm fido_cred_set_authdata_raw ,
.Nm fido_cred_set_attstmt ,
.Nm fido_cred_set_attobj ,
.Nm fido_cred_set_x509 ,
.Nm fido_cred_set_sig ,
.Nm fido_cred_set_id ,
.Nm fido_cred_set_clientdata ,
.Nm fido_cred_set_clientdata_hash ,
.Nm fido_cred_set_rp ,
.Nm fido_cred_set_user ,
.Nm fido_cred_set_extensions ,
.Nm fido_cred_set_blob ,
.Nm fido_cred_set_pin_minlen ,
.Nm fido_cred_set_prot ,
.Nm fido_cred_set_rk ,
.Nm fido_cred_set_uv ,
.Nm fido_cred_set_fmt ,
.Nm fido_cred_set_type
.Nd set parameters of a FIDO2 credential
.Sh SYNOPSIS
.In fido.h
.Bd -literal
typedef enum {
	FIDO_OPT_OMIT = 0, /* use authenticator's default */
	FIDO_OPT_FALSE,    /* explicitly set option to false */
        FIDO_OPT_TRUE,     /* explicitly set option to true */
} fido_opt_t;
.Ed
.Ft int
.Fn fido_cred_set_authdata "fido_cred_t *cred" "const unsigned char *ptr" "size_t len"
.Ft int
.Fn fido_cred_set_authdata_raw "fido_cred_t *cred" "const unsigned char *ptr" "size_t len"
.Ft int
.Fn fido_cred_set_attstmt "fido_cred_t *cred" "const unsigned char *ptr" "size_t len"
.Ft int
.Fn fido_cred_set_attobj "fido_cred_t *cred" "const unsigned char *ptr" "size_t len"
.Ft int
.Fn fido_cred_set_x509 "fido_cred_t *cred" "const unsigned char *ptr" "size_t len"
.Ft int
.Fn fido_cred_set_sig "fido_cred_t *cred" "const unsigned char *ptr" "size_t len"
.Ft int
.Fn fido_cred_set_id "fido_cred_t *cred" "const unsigned char *ptr" "size_t len"
.Ft int
.Fn fido_cred_set_clientdata "fido_cred_t *cred" "const unsigned char *ptr" "size_t len"
.Ft int
.Fn fido_cred_set_clientdata_hash "fido_cred_t *cred" "const unsigned char *ptr" "size_t len"
.Ft int
.Fn fido_cred_set_rp "fido_cred_t *cred" "const char *id" "const char *name"
.Ft int
.Fn fido_cred_set_user "fido_cred_t *cred" "const unsigned char *user_id" "size_t user_id_len" "const char *name" "const char *display_name" "const char *icon"
.Ft int
.Fn fido_cred_set_extensions "fido_cred_t *cred" "int flags"
.Ft int
.Fn fido_cred_set_blob "fido_cred_t *cred" "const unsigned char *ptr" "size_t len"
.Ft int
.Fn fido_cred_set_pin_minlen "fido_cred_t *cred" "size_t len"
.Ft int
.Fn fido_cred_set_prot "fido_cred_t *cred" "int prot"
.Ft int
.Fn fido_cred_set_rk "fido_cred_t *cred" "fido_opt_t rk"
.Ft int
.Fn fido_cred_set_uv "fido_cred_t *cred" "fido_opt_t uv"
.Ft int
.Fn fido_cred_set_fmt "fido_cred_t *cred" "const char *ptr"
.Ft int
.Fn fido_cred_set_type "fido_cred_t *cred" "int cose_alg"
.Sh DESCRIPTION
The
.Nm
set of functions define the various parameters of a FIDO2
credential, allowing a
.Fa fido_cred_t
type to be prepared for a subsequent call to
.Xr fido_dev_make_cred 3
or
.Xr fido_cred_verify 3 .
For the complete specification of a FIDO2 credential and the format
of its constituent parts, please refer to the Web Authentication
(webauthn) standard.
.Pp
The
.Fn fido_cred_set_authdata ,
.Fn fido_cred_set_attstmt ,
.Fn fido_cred_set_attobj ,
.Fn fido_cred_set_x509 ,
.Fn fido_cred_set_sig ,
.Fn fido_cred_set_id ,
and
.Fn fido_cred_set_clientdata_hash
functions set the authenticator data, attestation statement,
attestation object, attestation certificate, attestation signature,
id, and client data hash parts of
.Fa cred
to
.Fa ptr ,
where
.Fa ptr
points to
.Fa len
bytes.
A copy of
.Fa ptr
is made, and no references to the passed pointer are kept.
.Pp
The authenticator data passed to
.Fn fido_cred_set_authdata
must be a CBOR-encoded byte string, as obtained from
.Fn fido_cred_authdata_ptr .
Alternatively, a raw binary blob may be passed to
.Fn fido_cred_set_authdata_raw .
An application calling
.Fn fido_cred_set_authdata
does not need to call
.Fn fido_cred_set_id .
The latter is meant to be used in contexts where the
credential's authenticator data is not available.
.Pp
The attestation statement passed to
.Fn fido_cred_set_attstmt
must be a CBOR-encoded map, as obtained from
.Fn fido_cred_attstmt_ptr .
An application calling
.Fn fido_cred_set_attstmt
does not need to call
.Fn fido_cred_set_x509
or
.Fn fido_cred_set_sig .
The latter two are meant to be used in contexts where the
credential's complete attestation statement is not available or
required.
.Pp
The attestation object passed to
.Fn fido_cred_set_attobj
must be a CBOR-encoded map containing
.Dq authData ,
.Dq fmt ,
and
.Dq attStmt .
An application calling
.Fn fido_cred_set_attobj
does not need to call
.Fn fido_cred_set_fmt ,
.Fn fido_cred_set_attstmt ,
.Fn fido_cred_set_authdata ,
or
.Fn fido_cred_set_authdata_raw .
.Fn fido_cred_set_attobj
may be useful in applications interfacing with the WebAuthn API,
removing the need to first parse the attestation object to verify the
credential.
.Pp
The
.Fn fido_cred_set_clientdata
function allows an application to set the client data hash of
.Fa cred
by specifying the credential's unhashed client data.
This is required by Windows Hello, which calculates the client data
hash internally.
For compatibility with Windows Hello, applications should use
.Fn fido_cred_set_clientdata
instead of
.Fn fido_cred_set_clientdata_hash .
.Pp
The
.Fn fido_cred_set_rp
function sets the relying party
.Fa id
and
.Fa name
parameters of
.Fa cred ,
where
.Fa id
and
.Fa name
are NUL-terminated UTF-8 strings.
The contents of
.Fa id
and
.Fa name
are copied, and no references to the passed pointers are kept.
.Pp
The
.Fn fido_cred_set_user
function sets the user attributes of
.Fa cred ,
where
.Fa user_id
points to
.Fa user_id_len
bytes and
.Fa name ,
.Fa display_name ,
and
.Fa icon
are NUL-terminated UTF-8 strings.
The contents of
.Fa user_id ,
.Fa name ,
.Fa display_name ,
and
.Fa icon
are copied, and no references to the passed pointers are kept.
Previously set user attributes are flushed.
The
.Fa user_id ,
.Fa name ,
.Fa display_name ,
and
.Fa icon
parameters may be NULL.
.Pp
The
.Fn fido_cred_set_extensions
function sets the extensions of
.Fa cred
to the bitmask
.Fa flags .
At the moment, only the
.Dv FIDO_EXT_CRED_BLOB ,
.Dv FIDO_EXT_CRED_PROTECT ,
.Dv FIDO_EXT_HMAC_SECRET ,
.Dv FIDO_EXT_MINPINLEN ,
and
.Dv FIDO_EXT_LARGEBLOB_KEY
extensions are supported.
If
.Fa flags
is zero, the extensions of
.Fa cred
are cleared.
.Pp
The
.Fn fido_cred_set_blob
function sets the
.Dq credBlob
to be stored with
.Fa cred
to the data pointed to by
.Fa ptr ,
which must be
.Fa len
bytes long.
.Pp
The
.Fn fido_cred_set_pin_minlen
function enables the CTAP 2.1
.Dv FIDO_EXT_MINPINLEN
extension on
.Fa cred
and sets the expected minimum PIN length of
.Fa cred
to
.Fa len ,
where
.Fa len
is greater than zero.
If
.Fa len
is zero, the
.Dv FIDO_EXT_MINPINLEN
extension is disabled on
.Fa cred .
.Pp
The
.Fn fido_cred_set_prot
function enables the CTAP 2.1
.Dv FIDO_EXT_CRED_PROTECT
extension on
.Fa cred
and sets the protection of
.Fa cred
to the scalar
.Fa prot .
At the moment, only the
.Dv FIDO_CRED_PROT_UV_OPTIONAL ,
.Dv FIDO_CRED_PROT_UV_OPTIONAL_WITH_ID ,
and
.Dv FIDO_CRED_PROT_UV_REQUIRED
protections are supported.
If
.Fa prot
is zero, the protection of
.Fa cred
is cleared.
.Pp
The
.Fn fido_cred_set_rk
and
.Fn fido_cred_set_uv
functions set the
.Em rk
.Pq resident/discoverable key
and
.Em uv
.Pq user verification
attributes of
.Fa cred .
Both are
.Dv FIDO_OPT_OMIT
by default, allowing the authenticator to use its default settings.
.Pp
The
.Fn fido_cred_set_fmt
function sets the attestation statement format identifier of
.Fa cred
to
.Fa fmt ,
where
.Fa fmt
must be
.Vt "packed"
.Pq the format used in FIDO2 ,
.Vt "fido-u2f"
.Pq the format used in U2F ,
.Vt "tpm"
.Pq the format used by TPM-based authenticators ,
or
.Vt "none" .
A copy of
.Fa fmt
is made, and no references to the passed pointer are kept.
Note that not all authenticators support FIDO2 and therefore may only
be able to generate
.Vt fido-u2f
attestation statements.
.Pp
The
.Fn fido_cred_set_type
function sets the type of
.Fa cred to
.Fa cose_alg ,
where
.Fa cose_alg
is
.Dv COSE_ES256 ,
.Dv COSE_ES384 ,
.Dv COSE_RS256 ,
or
.Dv COSE_EDDSA .
The type of a credential may only be set once.
Note that not all authenticators support COSE_RS256, COSE_ES384, or
COSE_EDDSA.
.Pp
Use of the
.Nm
set of functions may happen in two distinct situations:
when generating a new credential on a FIDO2 device, prior to
.Xr fido_dev_make_cred 3
(i.e, in the context of a FIDO2 client), or when validating
a generated credential using
.Xr fido_cred_verify 3
(i.e, in the context of a FIDO2 server).
.Pp
For a complete description of the generation of a FIDO2 credential
and its verification, please refer to the FIDO2 specification.
A concrete utilisation example of the
.Nm
set of functions can be found in the
.Pa cred.c
example shipped with
.Em libfido2 .
.Sh RETURN VALUES
The error codes returned by the
.Nm
set of functions are defined in
.In fido/err.h .
On success,
.Dv FIDO_OK
is returned.
.Sh SEE ALSO
.Xr fido_cred_exclude 3 ,
.Xr fido_cred_verify 3 ,
.Xr fido_dev_make_cred 3
